Ultimately, the answer is a mystery, but some theories are shot down and others are suggested. One possibility is increasing obesity. Another is that marathons have turned into parties and shopping events.

I often bike in and around Balboa Park in San Diego. It has some hard hills to enjoy. I have noticed that most people in the park are not active and a substantial majority are over weight, including the children. On Friday evening the City brings in food trucks to feed them. Crowds flock to this event. The food is greasy, sugary stuff. People drive to the park to eat the bad stuff and then leave after resting from their meal. Increasingly, people move around the park not by walking, but by riding in electric carts.

It could be that wider participation is bringing down the average. That would be a good thing, not a bad one.

My own impression is that the population is dividing between people who are more fit and people who are less fit, than previously. And men, fit or unfit, seem to be bigger. When I was in high school, which was 1955-1959, many of the football players were in the range of 145-165 pounds. (Though I doubt they weigh that today, since I come from a town famous for its steak barbecues.) Or compare photos of American soldiers from WWII with ones now. Our soldiers now look like hulks, compared to the ones in WWII. Not exactly the build for runners, but I assume they are fit.

An interesting theory in that report is that the slower runners have caused some faster runners to abandon the big marathons.

That report comments briefly on the health effect of more participation by less fit runners. I have been struck by the large numbers of people who damage themselves at the SD R&R and need emergency medical attention. So many sirens.

Are we not seeing a similar thing on hiking trails. More unfit, unskilled hikers and more rescues? Don't the strongest hikers avoid the crowded places?

Hmmm. Interesting train of thought. I'm at a little bit of a loss on the definition though. When I ran the L A Marathon, I was in the top 4%. I thought that meant I was doing extremely well...then I ran an ultramarathon, and I barely made the top 50%! Comparisons are tricky, and stats are notoriously malleable, able to be worked into almost any point of view. If overall more Americans are doing marathons (I avoid the term "running" because many of the walkers doing the same distance make the runners look marvelous!) then there exists the real possibility that a larger number of people who are not necessarily very fit now choose to try to do a marathon, then the ultimate conclusion that I reach is that Americans are more motivated and more confident than ever. If we are talking about American professional athletes winning fewer marathons than we do in other races, I would hazard the guess that sprinting 100 meters with the aid of (undetectable) drugs and the most advanced technology ever seen analyzing the stride and performance of the athlete to optimize his/her success, then I would conclude that in marathons there is more of the old fashioned hard, gutsy training involved and less of the highly specific computer monitored performance of shorter events involved, and that yes, we Americans are still motivated and hard working, but perhaps less so than someone from another nation who values the win at a deeper level. What say you?

I read the article more carefully. The authors consider a number of explanations, such as more participation, higher ages, a higher percentage of women, and a higher percentage of walkers, perform statistical tests, and reject each hypothesis. But I don't think they ever considered them jointly, which is a different matter. Their wording strikes me as indicating an unscientific desire to arrive at their conclusion that lower average running times are due to increased obesity. The correlation is certainly there, and it may be true, but the sample size is small, and I think they need more evidence that the rise in obesity in the general population is also occurring in runners.

As I indicated earlier, I do see signs that many American men are morphing into hulks not built for running, but that is not the same as being obese or unfit.

Hi Z, i think you have captured the spirit of marathons, at least for many of us.

I am amazed by the speed and form of the winners. In the top 4%, I imagine your form and speed to be quite impressive too. I fully agree that performance unenhanced by drugs or computers is by far more impressive than enhanced performance.

Hi Ed, did you read the source article too? My take away was that the cause is a mystery, that the alternative theories (including weight gain) are unprovable and most interesting of all is that the slowing among men stands out.

Wildhorse, I assume you mean the article in your second link, yes, that was the one I read. It was interesting, but I object to an explanation being referred to as 'invalid' or a 'myth', because it statistically fails the test for being the full explanation. And the obesity variable is for the general population, they don't seem to have any obesity measure for runners. The results for men were interesting, and consistent with my casual and unsupported opinion that American men are moving in the direction of builds not great for running. But as I said, that is not necessarily the same as being obese or unfit, you see plenty of big men in fitness centers and on trails.

Yes, those are interesting observations, Ed. Your observation about the increasing bulk of men, reminds me too that men probably evolved for sprinting, not for marathons. That does not answer the question in article, of course. Just another observation.

Okay, having carefully perused both studies, I have to give them some points in how they drew their conclusions. There is one uninvestigated possibility, however...one that I have experienced, I was running a 50 k race a few years ago, and at some point my normal state of overdrive during a race faltered, and I thought, "I hate this. I am in terrible pain, feeling terrible stress, and it will yield nothing but a slightly faster time that no one in the world will care about but me. I am not going to win $1,000,000 or glory and honor for my country. This is nothing more than a personal test of my ability to stick with a project and do it well against all obstacles. Maybe I should apply this highly valuable part of my self-discipline to business instead of athletic races." So now, even when I am uninjured, I focus my training around my ability to contribute to the children and families I work for. If I do a better job for the rest of humanity and do a slightly slower job of finishing a marathon, the marathon has still done its job - it has taught me how to stick with a difficult task, maintaining focus and effort from start to finish. It has fulfilled it's purpose. And it has given me the ability to fulfill mine...which is taking care of other human beings besides myself. This is a better outcome than me finishing 309th in the LA Marathon instead of 310th. And it is more rewarding for me career-wise and allows me greater fulfillment as a man. If that's what's going on for everyone else, then maybe obesity is off the hook a bit and the lives of runners all across America have been improved. Hopin' that's the case!

Yes, Zip, that is an explanation worthy of consideration, that people are simply becoming more rational about integrating endurance sports into their overall lives, and less focused on achieving numbers. I would hate to be the researcher assigned to test that hypothesis, though. Some interesting explanations do not lend themselves well to statistical tests with existing data.

The researchers are Danish. Wonder if they have tried to replicate the same study for other countries.